Knowledge of the barometric, or atmospheric, pressure is desired in order to accurately perform control and diagnostic functions of an automotive power plant, including fuel injection and vapor purge controls. Although the barometric pressure may be measured directly with a dedicated sensor, many automotive manufacturers have relied on an estimate of the barometric pressure in order to save the cost of the sensor. The pressure estimation is typically based on the measured intake manifold pressure, with a variable adjustment or offset heuristically determined in relation to engine operating parameters such as speed and load. While this approach eliminates the sensor, the accuracy of the estimate tends to vary with operating conditions, and extensive calibration is required in order to provide acceptable accuracy at high altitudes. Accordingly, what is needed is an approach that is accurate over a wide range of operation and that requires only minimal effort to calibrate.